Patent GB-1147572-A (GB)
Title: Crosspoint network
IPC: H04Q3/00
Filed: 1968-01-11
Abstract: 1,147,572. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 11 Jan., 1968 [23 Jan., 1967], No. 1730/68. Heading H4K. A network comprising a matrix of relays energized over operate wires coupled to marking wires over diodes such as GA to GD, has a fault detector DET common to all marking wires in order to indicate any marking diode that has broken down and allows the busy potential on an operate wire to appear on the marking wires. Each set of marking wires is coupled to the detector over a diode, such as SA to SD, poled in opposition to the marking diodes. A connection is set up by putting positive battery on the operate wire inlet of stage D corresponding to a chosen junctor and by making contacts such as ma to md to connect the marking diodes in appropriate sections of the switching stages. With battery on the operate wire a diode GD conducts to energize winding Dr of a relay in the D matrix, a contact dr extending the operate wire into the C matrix. A C-relay will not energize until the marking contacts md are opened to take earth off the operate wire. C, B and A relays follow in similar fashion, the marker contacts mc. mb and ma being opened in succession. When the A relay responds it connects up a cut-off relay Cor which provides negative battery at the line circuit end of the operate wire. The junctor now connects earth from contact j and diode GJ and the marker retires. Busy links are thus indicated by negative battery on the operate wires. If the detector DET is of low impedance the idle condition of the links is indicated by negative battery connected over circuits shown in Fig. 4 in which an interrogation pulse passed by capacitor C to the junction of resistors R1 R2, is also passed by a diode G if the link is disconnected, the pulse being attenuated by G if the link is in a connection and carries negative battery. The pulse will also be attenuated by G and the link taken as busy if it is at earth or near earth. If the marking wires are multipled across all the inlets of a switch, as shown in Fig. 2 for a switch in the B stage, a faulty diode such as GB1], occurring in a connection which involves the associated relay, connects the earth from the fault detector DET by way of the marking wire m1 to the operate wire. Relays B, C and D in the connection are consequently short circuited and release the connection. The near earth connected to the inlet b of the matrix by the faulty diode busies the associated link to isolate the fault. If, however, the fault with diode GB11 occurs with a connection existing on inlet b1 and outlet a8, contacts br81 made, for example, the earth coupled from the detector and marking wire m1 to the link b 1 drains current away from the operated C and D stage relays to energize the winding Br11. The connection may still be held and the current in Br11 may not be sufficient to operate the relay but this relay will operate when the connection is normally released from the junctor; the C and D relays will fall back, but the B, A and Cor relays of the connection will remain operated to block both links and subscriber. If a connection also exists at this time which uses the outlet al, operation of contacts br11 forcibly releases the connection and blocks the outlet. If the fault occurs in an A-stage switch the operation of the associated A relay also operates a cut-off relay and blocks the subscriber. Should the current drained over a winding such as Br11 operate the relay without releasing an existing connection over inlet b1 then a double connection is set up if the outlet a1 is in use. To clear such faults the detector DET sets off an alarm and, either manually or automatically, contacts det0 are opened and det1/4 are closed to connect negative potential to all the marking wires to the switching stage C. All existing connections are thereby released along with fault operated relays. Contacts det1/4 open and det0 close to restore normal fault supervision and in particular to mark the link, such as b1 associated with a faulty diode, such as GB11, busy and isolate it from further connections set up over the network. Alternatively the detector may have a high impedance, the network links may be. marked idle by a positive potential, and the marking wires may be multipled over half the inlets of each matrix so that should a fault occur in a marking diode the resulting chaos will block only half the network, a degraded service being provided until in response to an alarm the fault is traced and rectified. The current supplied by the marker to the operate wire may be drawn from a constant current source. Marker contacts may be operated to prepare the operate circuits, the switching of current being effected with transistors.